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This study was undertaken to search for immune mediated mechanisms which could possibly be involved in the spontaneous regression of keratoacanthomas. In eleven patients with solitary keratoacanthoma, immunofluorescence studies did not reveal significant staining patterns, while skin tests, using autologous extracts of keratoacanthomas, were not compatible with true delayed cutaneous hypersensitivity reactions.

A 61-year-old woman is presented who developed numerous seborrheic keratoses within a few weeks. About 2 months later the patient noticed a progressive generalized erythematosquamous eruption on which the diagnosis of mycosis fungoides was made. PU-VA therapy resulted in complete remission of the mycosis fungoides lesions together with a resolution of the seborrheic keratoses. This is the third report of the Leser-Trélat sign in mycosis fungoides. The cases associated with malignant lymphomas are briefly reviewed.

Transplants of experimental keratoacanthomas induced in skin grafts which were in the growth phase of the hair follicle cycle (anagen phase) were carried out in immunocompetent and immunoincompetent receipients ("nude" mouse, nu/nu). No differences in gross graft observations were noticed. More than 80% of all keratoacanthomas disappeared postgrafting. This percentage was the same for both groups of recipients. These data are in keeping with a nonimmunological regression of experimental keratoacanthomas. A possible correlation with the hair follicle cycle is suggested.

In 9 rabbits, with a total of 17 experimental keratoacanthomas, a search has been made for immune-mediated mechanisms which could possibly be involved in the spontaneous regression of these tumours. Immunofluorescence studies did not reveal significant staining patterns. With skin tests, using autologous extracts prepared in three different ways, no delayed cutaneous hypersensitivity reactions were observed.

Telogen and anagen skin allografts of different ages were performed in congenitally athymic "nude" mouse recipients. After grafting, anagen skin allografts were more disturbed compared to telogen skin allografts. Consequently, when performing skin allografts attention should be paid to the hair-follicle cycle. In macroscopic and microscopic appearance allografts in the "nude" mouse were comparable to isografts as described in the literature for normal fur-bearing immune competent recipients.